Trend line
Draw and interpret trend lines on scatter plots in Grade 9 statistics: fit a line that best represents data direction without needing to pass through any point, then use it to make predictions.
Key Concepts
Property A trend line is a line on a scatter plot, which shows the relationship between two sets of data. It does not have to go through any of the points on the scatter plot.
Explanation A trend line is the 'best guess' straight path through your scattered data points. It doesn’t have to hit any dots, but it reveals the general direction—uphill for positive or downhill for negative—that your data is heading. It’s a quick visual summary of the relationship between your variables.
Examples For points (1, 5), (2, 7), (3, 6), and (4, 9), a trend line would be a straight line rising from left to right. A trend line with a positive slope like $y = 2x + 1$ indicates a positive correlation. A trend line with a negative slope like $y = x + 10$ indicates a negative correlation.
Common Questions
What is a trend line (line of best fit) on a scatter plot?
A trend line is a line drawn through a scatter plot that best represents the general direction of the data. It does not have to pass through any actual data points. About half the points should fall above the line and half below.
How do you draw an accurate trend line on a scatter plot?
Identify the general direction (positive or negative correlation). Draw a straight line through the data with approximately equal numbers of points above and below. The line should pass through the 'center' of the data cluster.
How do you use a trend line to make predictions?
Locate the x-value you want to predict on the horizontal axis. Draw a vertical line up to where it meets the trend line. Read the corresponding y-value from the vertical axis. This is your prediction (interpolation if within data range, extrapolation if outside).